(1) Field of the Invention
The present invention relates to an epoxy type particulate adhesive which contains a latent curing agent in the interior of the particles and is in the so-called B stage and which is cured by heating and functions as an adhesive, and a process for the preparation of this adhesive. More particularly, the present invention relates to a particulate adhesive which is substantially free of a solvent. It contains a latent curing agent homogeneously in the interior of the particles and is spherical and therefore, can be used especially advantageously for bonding electronic materials which are apt to be degraded by impurities and for which high-precision bonding is required, such as liquid crystal display plates.
(2) Description of the Related Art
Conventional epoxy type powdery adhesives are powdery mixtures of an epoxy resin powder formed by pulverizing an uncured or partially cured epoxy resin and classifying the pulverized resin if necessary and a latent curing agent powder. They are also powdery products obtained by pulverizing an uncured or partially cured epoxy resin with which a latent curing agent has been kneaded in advance and classifying the pulverized resin if necessary.
The conventional technique utilizing the pulverizing method is disadvantageous in that since respective particles are indeterminate in shape, the mobility of the powder is bad and the coating property is insufficient. In the case of bonding two plates, the distance between which is kept uniform by a spacer or the like, all the particles do not completely fill the space between the plates and there are many particles making no contribution to bonding.
A technique of spheroidizing particles formed by pulverization by passing them through a high-temperature atmosphere is known, but in case of particles containing a latent curing agent in the interior thereof, the curing reaction is advanced by this technique and therefore, it often happens that the adhesiveness is drastically degraded in the spheroidized particles.
The specification of U.S. Pat. No. 4,588,617 discloses a technique of forming cured particles having an average diameter smaller than 50 .mu.m by adding an amine type compound to an uncured epoxy compound emulsion prepared in advance. However, particles prepared according to this technique have no adhesiveness.
Another known technique is disclosed in Japanese Unexamined Patent Publication No. 57-29031, in which glass sheets are bonded and secured by using an encapsulated adhesive. However, this adhesive is poor in the bonding force and has bad influence on liquid crystals, and therefore, this adhesive is not preferred.